Alternating-current commutator-motor



E- F. W. ALEXANDERSON.

ALTERNATING CURRENT COMMUTATOR MOTOR.

APPLICATION FILED SEPT. H. 1914. 1,1 94,923. Patented Aug. 15,1916.

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E. F. W. ALEXANDERSON. ALTERNATING CURRENT COMMUTATOR MOTOR.

APPLICATION FILED SEPT. ll. 19H. 1,1 94,923. Patented Aug. 15,1916.

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ER IS/l VF. ALEX ANDERSGI'I. O

J. GTADEZ', NEW YORK, ASSIGNOR TO GENERAL EiiMUTRI -TZ CGMPAN'Z', ill. C-SRPOBATIQN 01 NEW YORK.

ALTERIHATDEG-CURRENT CGMlM'U'TATOR-BEOTOR.

Specification of Letters Patent.

Patented Aug. 15, 1916.

Application filed September 11, 1914. Serial No. 961,291.

T 0 all whom it may concern:

Be it known that I, Eunsr F. VJ. ALEX- nunnnson, a citizen of the United States, residing at Schenectady, county of Schenectady, State of New York, have invented certain new and useful Improvements in Alternating-Current Comn'nitator-hiotors, of which the following is a specification.

My invention relates to alternating current commutator motors, and more particularly to single phase alternating current motors having a cor nuted rotor winding of the direct current type and brushes arranged to provide a locally closed path for the current flowing in the commuted winding.

The object of my invention is to provide means for imparting to a single phase alternating current commutator mot r of the repulsion motor type a particularly desirable speed torque characteristic.

A further object of my invention is to provide means for improving the starting torque of alternating current commutator motors of the type to which my invention relates.

Again, the object of my invention is to provide means for modifying in a desired manner the speed torque characteristic of an alternating current commutator motor of the repulsion motor type so that the torque of the motor at low speeds may be increased, or so that the light load speeds of the motor may be limited.

More especially the object of my invention is to improve the speed-torque characteristics of the well known forms of repulsion. motors having for each pair of poles two sets, or an equivalent thereof, of shortcireuited brushes.

The features of my invention which believe to be patentably novel are definitely indicated in the claims appended hereto. The principle and mode of operation thereof and its application to alternating current motors f the repulsion motor type will'be understood from the following description taken in connection with the accompanying drawin gs, in which Figures 1, 2 and 3 are diagrammatic views of my invention applied to one particular form of repulsion motor; Figs. 8, 9 audit) are diagrammatic viei s of my invention applied to other forms of repulsion motor, and

Figs. 4, 5, (3, 7 and 11 are explanatory diagrams.

The aim of my present invention is to provide reliable and simple means for automatically modifying the speed torque characteristics of an alternating current motor of the repulsion motor type. My invention is more particularly concerned with motors of the repulsion motor type in which the brushes are shifted to vary the speed of the motor, and in such a motor I aim by my present invention to suitably modify the speed torque characteristics when the brushes are in their low speed positions, and particularly to increase the starting torque for these brush positions and to limit the light load speed of the motor. By the application of my invention to such a motor, the speed torque characteristic of the motor is modified only at abnormal speeds, as when the motor is starting or at relatively high light-load speeds, while at all normal running speeds the speed torque characteristic of the motor is not substantially altered. As is well understood, the repulsion motor comprises an inducing winding and an in duced winding with a principal or main short-circuit about the induced winding along an axis at an angle to the inducing or working axis. In accordance with my present invention, I provide an auxiliary local circuit for the induced winding along an axis at right angles to the axis of the principal short-circuit, and I include in this auxiliary local circuit an inductive winding having a magnetic circuit designed to become magnetically saturated at a predetermined voltage.

My invention will be better understood by a brief consideration of certain forms of repulsion motors embodying the same.

The motor diagrammatically represented in Figs. 1, 2 and 3 of the drawings is a well known form of alternating current motor of the repulsion motor type, having two sets of relatively movable short-circuited brushes associated with the rotor or armature member. An inducing winding 10 is arranged on the stator member of the motor and is adapted to be connected to a single phase source of alternating current 11. The rotor member of the motor carries an induced or armature winding 12. The induced winding is a commuted vinding ot the direct current type, and is, accordingly, appropriately connected to the segments of a conimutatm' upon which are operatively positioned the commutator brushes. The commutator brushes are. divided into two sets, each set comprising a stationary and a movable brush. The stationary brushes are located in the magnetizing axis of the inducing winding, while the movable brus ies are an ranged along an axis at an angle to the axis of magnetization of the inducing winding. In Figs. 1, 2 and 3 of the drawings, 1 have illustrated a bi-polar motor and, accord inglv, there are two stationary brushes 13 posi ioned in the magnetizing axis of the inducing winding 10. Each stationary brush has a cooperating movable brush Lt con nected thereto by a short-circuiting *on ductor 15. As is well understood in the art, the brushes 14: are moved to obtain the desired speed regulation of the motor, the movement of the brushes ll being such that they are always maintained (in a two-pole design) diametrically opposite to one an other. Four positions of the movable brushes are indicated in Fig. l of the drawings. The brush position H. is a low speed brush position, and the brush position LP is a high speed brush position, while brush positions ll and ll are intermediate stages. In all of the figures of the accompanying drawings 1 have represented stationary brushes by shading lines, while movable brushes are unshaded.

The principle of operation and the characteristics of the motor described in the preceding paragraph are well known. The purpose and mode of operation of my present invention will, however, be more clearly understood after a brief discussion oi. certain.

general characteristics of repulsionemotors. In motors of the repulsion motor type, a current fiowing in the inducing winding induces by t 'austormer action a tin-rent in the induced winding. The induced winding is closed through the principle or main shortcircuit in such a manner that the axis of magnetization of the induced winding with respect to this short-circuit is at an angle to the axis of magnetization of the inducing winding, hereinafter called the inducing or working axis. The magnetization produced by the induced winding may be resolved into two components, one in line with the inducin g axis and the other at right angles thereto. The latter component represents the torqueproducing field of the motor and may be produced by the inducing winding alone or by the inducing and induced winding together. The component of the induced winding magnetization in line with the inducing axis represents the energy or working current of the motor. It vill be evident that the axis of magnetization of the indueed winding with respect to the principal short-circuit is coincident with the. inducing axis, ti o motor has no torque producing field, and also that as this axis ot magnetization of the induced winding moves away from the inducing axis, the tor ireproducing lield inc cases while the energy current decreases, until these two axes are at right angles to each other, when the torque-producing field oi the motor is a maximum and the energy current is a minimum or substantially zero. The strength of the torque-producing field is thus determined by the angle between the inducing axis and the axis of magnetization of the induced winding with respect to the principal short-circuit about the latter.

Shifting the brushes connectal to the principal short-circuit of a motor of the repulsion motor type shifts the axis of magnetization ot' the induced winding and varies the torque-producing field of the motor, thereby changing the speed of the motor. ll' hen the torquepreducing field is of small. strength the speed will be high. while when this field is of large strengththe speed will be low. When the brushes are in their low speed positions, the motor field strength is thus large, and as a result the inducing winding has considerable reactance, which chokes the flow of current therethrough and limits the energy current of the motor. It the induced w -ding is closed through an auxiliary local circuit along an axis at right angles to the axis of the principal short-circuit, a current path is provided for a current whose magnetizing etfect is to modify the torque-prmlucing field oil": the motor. The auxiliary local short-circuit has two eilects; first, it alters the field strength of the motor, and, second, it alters the reactance of the inducing winding, due to the change in the field strcngtl and thereby modifies the energy current of the motor. llhen the brushes of the principal slant-circuit occupy their low-speed positions, the auxiliary local short-circuit operates at low speeds, first. to decrease the strength of the torque-producing field ot the motor, and, second. to reduce the reactance of the inducing winding and to permit the flow or an increased energy cur rent. The voltage between those points of the induced winding to which the auxiliary short-circuit is electrically connected is a function of the speed of the motor. rt s fnchronous speed this voltage is zero, and the voltage gradually increases as the speed *aries either way from s cl ronous speed,

being a maximum at standstill and relatively large at speeds considerably above swan-hmnous.

The speed torque curves oi a reyulsion motor of the type represented in Figs. 1, 2 and are shown in Fig. (3 of the drawings. The curve indicated by reference numeral 1 14. is the speed torque curve of the motor when the movable brushes occupy the position 14 of Fig. 1, which is a high speed or normal running position of the movable brushes. Curves 14:3, 142 and 1 11 are the speed torque curves corresponding to the brush positions 14;, i l and 14:, respectively. It will be observed that in the brush position 14 the normal running speed is somewhat higher than synchronous speed, which is indicated by the horizontal line ss. The starting torque for this brush position is very considerably greater than the normal running torque. On the other hand, in the low speed brush position 14 the speed is lower than synchronous speed for the same running torque. It will be seen that the speed torque curve lll is of such a character that the starting torque is only slightly higher than the normal running torque for this corresponding brush position 14. It will thus be evident that in this low speed position of the brushes, the torque of the motor is relatively small, and hence it the static friction of the load to be driven is very high it may not be possible to start the load with the brushes in the low speed position, but instead it will be necessary to start with the brushes in the high speed position, and then after the motor is running up to speed to move the brushes back to the desired low speed position. One of the objects of my present invention is to overcome this difficulty, and to provide means whereby the speed torque characteristics of the motor can be controlled and modified to give a satisfactory starting torque when the brushes are shifted to the low speed positions.

In accordance with my present invention, an inductive winding or reactance is included in an auxiliary local circuit about the induced winding. The axis of this local circuit is electrically in quadrature to the axis of the principal short-circuit. The in ductive winding has a magnetic circuit designed to become magnetically saturated at a predetermined voltage. This predetermined voltage is selected so as to limit the voltage between those points of the induced winding to which the inductive winding is electrically connected when the main brushes are in low speed positions to a value which is permissible from the point of'view of voltage induced per commutator segment, and to a value which limits the choking effect of the torqueproducing field. When the voltage between those points of the induced winding to which the inductive winding is electrically connected is such that the magnetic circuit of the inductive winding is magnetically saturated, the inductive viiuiling will have a relatively low impedance, and a very large current will flow therethrough. The flow of this relatively large current through the inductive winding at low speeds decreases the torque-producing field of the motor and increases the energy current. The increase in energy current is considerably greater than the decrease in field strength, and, since torque is proportional to the product of the energ' crurent into the field strength, an increased torque of the motor is efi'ected. 1V hen the voltage between those points of the induced winding to which the inductive winding is electrically connected falls below the saturation voltage, for example as the motor speeds up after starting, the inductive winding acts as a choke coil of considerable impedance, and limits the flow of current therethrough to a relative small value. It will thus be evident that an inductive winding connected as described and having a predetermined saturation voltage determined in accordance with the principle of my invention is automatic in its action, and has no or very slight influence on the operation of the motor at normal running speeds, in the vicinity of synchronism, while at very low speeds and at very high speeds the effect of this inductive winding is very pronounced, due to the saturation of its magnetic circuit. A saturated inductive winding designed so as to limit the field strength at standstill and at relatively high speeds to a certain definite value will have this limiting effect only when the magnetic circuit of the winding is saturated, as at standstill or at relatively high speeds. The saturated inductive winding thus allows the motor field to increase in strength gradually as the motor speeds up. This automatic and gradual increase of field strength is exactly what is wanted during the. starting of the motor in order to get the desired characteristics in commutation as well as relation between speed and torque.

In carrying out myinvention in a motor of the type represented in Figs. 1, 2, and 8, I connect a reactive coil having a magnetic core designed to become magnetically saturated at a predetermined voltage value, between the two sets of short-circuited brushes 1314. In Fig. 1 of the drawings I have illustrated such a reactive coil comprising a winding 16 connected between the short-circuiting conductors 15 and inductively interlinked with a magnetic circuit 17. The magnetic circuit 17 is so designed that it will become magnetically saturated when a predetermined voltage exists between the short-circuiting conductors 15, which voltage is so selected that saturation is attained at the starting of the motor, thus permitting a relatively large amount of current to flow through the winding 16. The current flowing in the inducing winding 10 induces by transformer action a current in the induced winding 12. The brush arrangement is such that the energy or work- -n o the ind correspoinh thcrilo is susta a neutralii-itd lrv magnetization produced hy the enerlji' or working current. The niagne raition one to the current flowing i or .on of the inducing winding which corresponds to the portion oi the induced winding he .veen the two it short-circuited hrus ies is not neutralized by the currents flowing in the induced .vindin and hence is citective to establish afield 101 the motor. It will thus be seen that the short-circuitingconductors l5 irovide short-circuits for the induced winding along an axis at an angle to the magnetizing axis of the inducing winding. and that the inductive winding connected in an auxiliary local circuit along an axis at -1 angles to the axis of the principal or i short-circuits. The inductive winding is thus connazted alone t l lt axis of the inluct terlinlzed with the l l winding which is in t torque producing tield oi the motor. and the =ll'ect ot the inductive \Yllltllllg whe so eontor ue producing ,c ield.

The F i (tors rep an 1 1e drawings determined h angle emhraced between a stationar; lnush 1 3 and tie movahle hrush Ll of the ad acent shortcircuited set ot hrushes. and hence when the movable brushes are shifted to a position near the stationar hrushes of the adjacent short-cireuited set of brushes, the torque producing field of the motor is relativel small. and when tl e movahle hrushes are shifted a relatively great distance from the stationar hrushcs ot' the adjacent shortcircuitcd set of lu'ushes. the torque producing field is relativclv large. "ihe latter position ot the mov: lllG hrushes are their low speei positions 211R, due to the large torqueproducing field which exists when the brushes occup such positions. the inducing winning will have conside able rcactance, which cholres the how of current therethrough. and results in diminishing the ene' 'v current of the motor. The local ai xiliarv circuit including the inductive winding connected between the se of short-circuited n'ushes provides a current path for that portion of the induced windinc which is interlinked with the torque producing n-"ld Hit the motor. it current thus: flows i i that portion of the induced winding interlinl-zed with the torque producing: iield o'l the motor. and this current partialli' neutral 170% the etlect of the current flowing in that nortioi it the induci ing winding interlinked with the m itor field, whereh} the motor field strength is demotor field ie reactant-c oi the undueierniits a larger current to 1, 'here rv increasing creased. strength mg w" t s oi? shortthe. anQle is o't short-circuited a function oi the and is further s iced if the motor. At synchronous soeed this voltage is zero, and the voltage gradustrong iield results in destructive s at-king at the commutator brushes, and. due to tl a i incre sed reactance of he inducing wn din tends to reduce the magnitude ot the enei ci rrent in the motor. in :mcordance with the principle of my present invention, the

magnetic circuit ot the inductive winding is designed to heciine magneticall v saturated at such a voltage value as to suitably limit the choking eii'ect ot' the torque producing iield and to restrict the volta e induced per commutator segment to a perinissihle value. When the voltage hctween tne two sets of short-circuited lnushes to which the inductive winding connected is such that the magnetic circuit of the inductive winding is mag ietlcally saturated. the inductive vindf ing' will have relatively low impedance. and a very large current will flow therethrough. The tlow of this relatively large current through the inductive windingduring the starting of the motor decreases the torque producing field of the motor and suits in increasing the energg' current. iihen the voltage hetween the two sets of short-circuitcd brushes falls helow the saturation voltage, for exampl as the motor :peeds up after starting. the inductive winding acts as a choke coil of considerable impedance. and limits the flow of current therethrough to a relatively small. value. It will thus he evident that the ell' ect of the saturated inductive winding in modifying the torque producing held of the motor is auton'iatic. since the torque prcducing field onlv materiall v modified when the magnetic circuit oi? the nductive winding is saturated as: at standtill or a relatively high speed v The inaglnetixiiur curve oi? the winding 16 of Fig. l is shown i i the drawings. ilurinc the staitinc (iii the motor the magnetic circuit 17 is worked at the point of saturation. for example in the lilvicinity of the point marlzed S, and the he voltage between the two sets oiductive winding therefore acts to provide a local current path about the induced winding of relatively low impedance. As the motor speeds up, the voltage between the points of the induced winding to which the inductive winding is electrically connected, that is across the two sets of short-circuited brushes, diminishes, and hence the current flowing in the local circuit including the inductive winding decreases, whereupon the magnetic circuit 17 no longer saturated, and the inductive winding in this condition acts as a choke coil of relatively high impedance, so that at the normal running speeds of the motor little or no current flows in the inductive winding circuit. During the normal running of the motor the magnetic circuit 17 is worked in the vicinity of the point B.

The eli'ect of the inductive Winding upon the speed torque curves of the motor is illustrated in Fig. 7. The curves 114, 214, 314 and 414 correspond to brush positions 14, 14, 14", and 14 and to curves 141, 142, 143 and 144 of Fig. 6. It will be evident upon examination of the curves of Fig. 7 that even in the low speed positions of the brushes the starting torque of the motor will be very much greater than the normal running torque for this brush position, and sulliciently large to start any load that a motor of this type is likely to be connected to. The saturated reactive coil is most beneficial for the low speed brush positions, and in these brush positions increases the torque range of the speed torque curve so that the motor has a relatively high starting torque, and a starting torque very considerably greater than obtained when the reactance is not employed. \Vhcn the relatively movable brushes are shifted near together, which corresponds to the maximum full-speed of the motor, the inductive winding lies across a very small angle of the induced winding, and the voltage induced between the two sets of short-circuited brushes will not be high, even with a very high speed of the mo tor. For this reason the saturated inductive winding is most effective when the brushes are in the low speed positions, and it is with these positions of the brushes that my invention is more particularly concerned.

I may also ll'l'lPlOV6 the power factor of the motor by using for the inductive winding the secondary winding of a series transformer, the primary winding of which is connected in series with the inducing winding of the motor. This modification of my invention is illustrated in Fig. 2 of the drawings. In this figure I have illustrated a transformer having a primary winding 18 connected in series with the inducing winding 10 and a secondary winding 19 connected between the sets of short-circuited brushes. It will of course be understood that the transformer may take the form of a compensator in which case a single transformer winding will be employed, as is well understood in the art. The magnetic circuit 20 of the transformer is designed to becomemagnetically saturated by the starting current of the motor in exactly the same manner as heretofore explained in connection with Fig. 1. The phase of the electromotive force induced in the secondary winding 19 of the transformer and impressed on the two sets of short-circuited brushes is such that a power factor compensation is obtained as will be understood by those skilled in the art.

Another means for obtaining an improved power factor in connection with my invention is illustrated in Fig. 3 of the drawings. In the modification shown in this figure an inductive winding 21 is connected in series with a source of shunt excitation and across the two sets of short-circuited brushes. In this figure I have shown an arrangement whereby the desired shunt excitation is obtained from the inducing winding of the motor although of course it will be understood that a separate winding inductively related to the inducing winding or an independent source of electromotive force may be employed if desired. \Vhen the shunt excitation is supplied by the inducing winding the phase position will of course be suitably chosen to give a current of the proper time phase. In using the arrangement of Fig. 3, it is necessary to build the reactance with an open magnetic circuit 22 so that there will be a certain amount of shunt excitation at any speed, regardless of the voltage across the short-circuited brushes. The magnetizing curve of the magnetic circuit 22 is shown in Fig. 5. It will be noted that there is no sharp bend in this curve and saturation is gradually approached rather than abruptly, as in the cases of the inductive winding and the series transformer. The magnetic circuit is worked during the starting of the motor in the vicinity of the point S, while during the normal running of the motor the circuit is worked in the vicinity of the point It.

In Fig. 8 of the drawings I have diagrammatically illustrated my invention applied to a slightly modified form of single phase alternating current commutator motor of the repulsion motor type. In this form of motor'the brushes are arranged in quadrature and are all movable as a unit, being preferably carried by the same brush yoke. Thus, brushes 23-23 and brushes 24-24 correpond to brushes 1313 and brushes 14-14, respectively, of the meters of igs. 1, 2 and 8 of the drawings, and the principle of operation of the motor represented in Fig. 8 is substantially the same as that of the motor illustrated in the first three figures. A

transformer winding 19 connected in series relation with the inducing winding 10 has its terminals connected across the two sets of short-circuit-ed brushes just as in Fig. 2 of the drawings. It will be understood that the magnetic circuit of the transformer' winding is designed to become magnetically saturated when the voltage between the brushes to which the transformer winding connected attains a predetermined value.

Fig. 9 of the drawings diagrammatically illustrates my invention applied to a still diil'erent term of repulsion motor. This motor has a stator winding 10 and a commuted armature winding 12 ot' the same character as described in connection with the motors of Figs. 1, 2, 3 and S. l he brushes in the motor of Fig. 9 are arranged in electrical quadrature, and one set of oppositely positioned brushes are directly short-circuited along an axis at an angle to the magnetizing axis of the inducing winding, while the other set of oppositely positioned brushes 3&3i are closed through the inductive winding 16 along an axis electrically in quadrature to the axis of the main short-circuit. The magnetic circuit 17 of this inductive winding 16 is designed to become magnetically saturated when the speed of the motor is such that a predetermined voltage exists between the brushes All of the brushes in this form of motor are mounted upon the same brush yoke, and are hence movable as a unit to obtain the desired speed regulation of the motor.

In Fig. 10 ot the drawings I have shown the inductive winding 16 of Fig. 9 of the drawings replaced by the secondary wind ing 19 of a series transformer, in order to obtain power factor compensation of the motor. The magnetic circuit of the transformer is designed to become magnetically saturated when a. predetermined voltage exists between the brushes 3-l-3l, and the t'unction and operation of the transformer is the same as described in connection with Fig. 2. It will be evident that the main brushes of the motors represented in Figs. 9 and 10 of the drawings provide a principal short-circuit for the induced winding along an axis at an angle to the magnetizing axis of the inducing winding, and that the auxiliary local circuit through the inductive winding, such as the winding 16 of the winding 19, is along an axis electrically at right angles to the axis of the principal short-circuit.

In Fig. 11 of the drawings I have shown in full lines, for the purpose of comparison, a speed torque curve of a character sub stantially general to single phase alternatingcurrent commutator motors of the type to which my invention relates, and in dotted lines a. speed torque curve of such a motor embodying my invention. Synchronous speed is indicated by the horizontal line ss. It will be noted that the application of my invention to such a motor modifies the speed torque curve of the motor at relatively low and at relatively high speeds. The voltage between the brushes to which the inductive winding of my invention is connected is substantially zero at synchronous speed. is the speed of the motor varies from synchronous speed in either direction the voltage between these brushes increases. Thus at relatively low speeds and at relatively high speeds. the voltage between these brushes is sulliciently large to cause the mark netic circuit of the inductive winding to become magnetically saturated, whereupon a relatively large current [lows through the inductive winding. Thus at relatiiely low speeds my invention operates to increase the torque of the motor, while at relatively high speeds my invention operates to diminish the motor torque. That is, at relatively high speeds, or at light loads, my invention operates to limit the speed of the motor, and prevents the motor running away. where its normal characteristics are such that it has this tendency.

It will be evident from the foregoing description. that I have provided an arrangement of apparatus whereby the speed torque curve of a commutator motor of the repulsion motor type may be zulvantageously modified. Thus, in accordance with my invention the starting torque of the motor may be increased with reference to the running torque. and the light load speed ot the motor may be suitably limited when desired. Incidentally, my present invention is also advantageous in preventing sparking at starting because the same amountof starting torque will be obtained with a large working current and small field strength.

irlthough the invention has been more particularly described wita reference to a two pole motor with a rew lving induced member, still it will be understood that the invention is egually well applicable to motors having any number of pole pairs, and that the 'nduced instead of the inducing member may be stationary. have plained my invention by diagrammaticallv illustrating and describing certain specific embodiments thereof, but it will be readily understood by those skilled in the art that the invention may be embodied in many other forms than that shown and described. I, accordingly, do not wish to be restricted to the particular form and construction disclosed her in by way of example for the pur pose of setting forth my invention in accordance with the patent statutes. The terms of the appended claims. therefore, are not restricted to the precise structure disclosed, but are intended to cover all changes and modifications within the spirit and, scope of my invention, and it will hence be understood that my invention may be embodied in practice in various other ways than that herein illustrated and described and still be within the purview of the claims appended hereto.

hat I claim as new and desire to secure by Letters Patent of the United States, is:-

l. A single phase alternating current con'in'iutator motor having an inducing winding and an induced winding, a commutator connected to said induced winding, brushes bearing on said coinnnitator, certain ol' said brushes being connected to form a main short-circuit about the induced winding along an axis at an angle to the magnetizing axis of the inducing winding, an inductive winding connected between certain of said. brushes to form a local circuit about the induced winding along an axis in electrical quadrature to the axis of said main short-circuit, said inductive winding having a magnetic circuit designed to become magnetically saturated when a predetermined voltage exists between the brushes to which said inductive winding is connected.

2. A single phase alternating current commutator motor having an inducing winding and an induced winding, a commutator connected to said induced winding, brushes bearing on said commutator, certain of said brushes being connected to form a main short-circuit about the induced winding along an axis at an angle to the magnetizing axis of the inducing winding, a transformer having its primary winding connected in series with said inducing winding, the secondary winding of said transformer being connected between certain of said brushes to form a local circuit about the induced winding along an axis in electrical quadrature to theaxis of said main short-circuit, said transformer having a niiagnetic circuit designed to become magnctically saturated when a predetermined voltage exists between the brushes to which the secmidary winding is connected.

3. A single phase alternating current commutator motor having an inducing winding and an induced winding, a connnutator connected to said induced winding, brushes bearing on said commutator, certain of said brushes being connected. to form a locally short-cir mited path for the current flowing in said induced winding, and an inductive winding connected between certain of said brushes and adapted to provide a local circuit about the induced winding along an axis which is interlinked with the torque producing field of the motor, said inductive winding having a magnetic circuit adapted to become magnetically saturated when a predetermined voltage exists between the brushes to which said inductive Winding is connected 4 4. A single phase alternating current commutator motor having an inducing winding and an induced winding, a commutator connected to said induced winding, brushes bearing on said commutator, certain of said brushes being connected to form a locally short-circuited path about the induced winding, and an inductive winding connected between certain of said brushes and having a magnetic circuit adapted to become magnetically saturated when a predetermined voltage exists between the brushes to which said inductive winding is connected.

A single phase alternating current commutator motor having an inducing winding and an induced winding, a commutator connected to said induced winding, brushes bearing on said commutator, certain of said brushes being connected to form a main short-circuit along one axis of said induced winding, and an inductive winding connected between certain of said brushes along an axis of said induced winding electrically in quadrature with the axis of the main short-circuit, said inductive winding having a magnetic circuit designed to become magnetically saturated when the speed of the motor is such that a predetermined voltage exists between the brushes to which said inductive winding is connected.

6. A single phase alternating current commutator motor having an inducing winding and an induced winding, a commutator connected to said induced winding, brushes bearing on said commutator, certain of said brusl es being connected to form a main short-circuit along one axis of said induced winding, and a transformer winding con- 11 cted in series relation with said inducing winding and between certain of said brushes along an axis of said induced winding electrically in quadrature with the axis of the main short-circuit, said transformer winding having amagnetic circuit designed to become magnetically saturated when the speed of the motor is such that a predetermined voltage exists between the brushes to which said inductive winding is connected.

7. A single phase alternating current commutator motor having an inducing winding and an induced winding, a commutator connected to said induced winding, brushes bearing on said commutator, certain of said brushes being connected to form a main short-circuit about the induced winding along an axis at an angle to the magnetizing axis of the inducing winding, an inductive windingconnected between certain of said brushes to form a local circuit about the induced winding along an axis electrically in quadrature to the axis of said main short-circuit, said inductive winding having a magnetic circuit designed to become magnetically saturated when a predetermined voltage exists between the brushes to which said inductive winding is connected, and means whereby a power factor compensating electromotive force may be impressed upon said induced winding through the brushes to which said inductive winding is connected.

8. A single phase alternating current commutator motor having an inducing winding and an induced winding, a commn tator connected to said induced winding, brushes bearing on said commutator, certain of said brushes being connected to form a locally short-circuited path for the current liowing in said induced winding, and a transformer winding connected in series relation with said inducing winding and between certain of said brushes and having a magnetic circuit adapted to become magnetically saturated when a predetermined voltage exists between the brushes to which said inductive winding is connected.

9. A single phase alternating current commutator motor having an inducing winding and an induced winding, a commutator connected to said induced winding, brushes bearing on said commutator, certain of said brushes being connected to form a locally short-circuited path for the current flowing in said induced winding, an inductive winding connected between certain of said brushes and having a magnetic circuit adapted to become magneticall saturated when a predetermined voltage exists between the brushes to which said inductive wini'liug is connected, and means whereby a power factor compensating electromotive force may be impressed upon said induced winding through the brushes to which said inductive winding is connected.

In witness whereof, I have hereunto set my hand this 10th day of September, 19H.

ERNST F. \V. ALEXANDE ISON. lVitnesses:

BENJAMIN HULL, HELEN ORFORD.

Copies of this patent may be obtained for five cents each, by addressing the Commissioner of Patents,

Washington, D. C. 

